The surface of the interior of dishwashers becomes covered with residues over the course of time. The kind of residues found most frequently are: limescale, soap scum and food deposits. Limescale is formed from the insolubilisation of ions contained in tap water. The limescale deposits in the dishwashing interior especially in the heater elements of the dishwasher. Such deposits are undesirable not only from the aesthetic aspect but also because they can interfere with the heat exchange process and this results in less efficient use of energy. The soap scums are remnants from the detergents. The food deposits mainly consist of finely divided fatty food residues and they are usually found in the filter giving it a greasy appearance.
Some dishwashing interior cleaning compositions have been formulated, however they are mainly aimed at limescale removal rather than the removal of greasy residues. These compositions moreover, are generally in the form of liquids or granules. Tablets are considered a more convenient form, however, a dishwasher interior cleaner in tablet form is not apparently known in the art. It is understood that cleaning compositions in tablet form hold several advantages over cleaning compositions in particulate form, such as ease of dosing, handling, transportation and storage. Therefore, there is a need for a dishwashing interior cleaning compositions in tablet form.
The use of acidic cleaning compositions to remove limescale is well-known in the art (See for example U.S. Pat. No. 5,733,859, EP-A-0,496,188 and EP-A-0,601,990). U.S. Pat. No. 5,877,132 discloses an aqueous cleaning composition for removing limescale from surfaces wherein said composition comprises a biodegradable aqueous acidic system, preferably a surfactant and additional components selected from thickeners, co-builders and enzyme mixtures. Said enzyme mixtures comprises carbohydrase and gluconase enzymes. Liquid and granular acidic compositions are traditionally used to clean the interior of automatic dishwashers. EP-A-0,256,148 discloses a cleaner composition for dishwashing machine interiors comprising citric acid and low-foaming non-ionic surfactant. U.S. Pat. No. 5,981,449 discloses an aqueous cleaning composition for removing limescale in automatic dishwashers and laundry machines. The cleaning composition comprises maleic acid and an acid-stable thickener. U.S. Pat. No. 4,465,612 describes a process for cleaning and maintaining dishwashing interiors. The cleaning composition is a liquid containing an acid, an alcohol a low-sudsing non-ionic surfactant and customary additives.
EP-A-0,612,843 discloses a process for granulating acidic crystalline material. The granules are used in formulating a granular acidic cleaner used to clean dishwashing machine interiors. The cleaning compositions may be in unit-dose twin-compartment pack form comprising a weak organic acid such as citric acid, non-ionic surfactant, a strong organic acid, such as sulphamic and a perfume.
The present invention thereafter provides machine cleaner in tablet form having improved cleaning performance on machine filters as well as good limescale removal performance and product stability.